Controls for variable pumps or motors

ABSTRACT

Disclosed is a variable displacement hydraulic pump or motor control system of the type including a servo motor which is responsive to movement of a pilot control element for controlling the displacement of the pump or motor. Means are provided for operating the pilot control element in response to the setting of a manual displacement control and in response to a signal from an overriding control means to override the manual displacement control. The overriding control operates through a second servo motor for varying the position of the pilot element.

United States Patent [1 1 Ifield [451 Nov. 12, 1974 CONTROLS FOR VARIABLE PUMPS OR MOTORS [75] Inventor: Richard Joseph Ifield, Dural, New

South-Wales, Australia [73] Assignee: Advanced Products Pty. Limited,

Dural, New South Wales, Australia [22] Filed: July 24, 1972 [21] Appl. No.: 274,691

[30] Foreign Application Priority Data July 28, 1971 Australia 5697/71 [52] US. Cl 91/497, 417/218, 60/427, 60/444 [51] Int. Cl. F04b 1/26 [58] Field of Search 417/218, 222;

[56] References Cited UNITED STATES PATENTS 3,017,750 1/1962 Kempson 417/218 Young 60/427 3,163,115 12/1964 Neff et al.'. 417/222 3,164,960 1/1965 Weisenbach et al 417/222 3,199,286 8/1965 Anderson 60/452 3,252,426 5/1966 Parr 417/222 3,384,027 5/1968 Jennings et al.. 417/218 3,593,523 7/1971 Flaschar H 60/427 Primary ExaminerWilliam L. Freeh [57] ABSTRACT Disclosed is a variable displacement hydraulic pump or motor control system of the type including a servo LELQIL E LiSLQ QEE XSJQ1 92 of a P t control element forcontrolling m disfia cetfint of the pump or motor. Means are provided for operating the pilot control element in response "to the setting of a manual displacement control and in response to a signal from an overriding control means to override the manual displacement control. The overriding control operates through a second servo motor for varying the position of the pilot element.

7 Claims, 4 Drawing Figures PATENIEBHBMW I 3547.061

sum HP 3 PATENTEDNUY 12 1914 $847,061

sum 2 or a CONTROLS FOR VARIABLE PUMPS OR MOTORS This invention is related to variable displacement hydraulic pumps and motors as employed in hydraulic power transmission systems and of the type where the displacement of the pumps and motors are varied by a servo motor, the movements of which and hence the displacement of the pump or motor, being responsive to the position of a pilot control element, such as a rod, lever or rotary valve knob. The invention is concerned with the means for operating the said pilot control element in response to the setting of a manual displacement control or in response to overriding control signals.

In a hydraulic transmission of the type referred to, it is desirable to fulfil many control and override requirements as follows:

a. The displacements must be manually variable to determine the maximum displacement of the pump and the minimum displacement of the motor, thereby to determine the highest motor speed for a given pump speed.

b. Overriding devices are preferably provided, to cause the motor displacement to increase above the setting of the manual control, when the drive transmis sion pressure exceeds a predetermined maximum value and to cause the pump displacement to decrease below the setting of the manual control, when the drive trans- Hitherto the pilot element has been employed as the manual displacement control element and overriding devices have been in the form of pressure operated dead beat valves, acting directly on the pressures at the servo motor to override the setting of the manual control. Such high pressure overriding valves are expensive high precision devices subject to erosion and abrasive wear and liable to become unstable in service, furthermore such valves are not easily adapted to meet some of the requirements, such as those discussed at (e), (f) and (g).

An object of the invention is to provide simple means for satisfying such of the foregoing requirements as may be needed in any particular hydraulic transmission of the type under discussion. That object is achieved by the provision of a primary servo motor, preferably powered by the boost pressure, responsive to the overriding devices and operating the main servo motor through the beforementioned pilot element; the overriding devices being simple low pressure valves responding to the overriding signals.

The invention consists in a control system for variable displacement pumps or motors of the kind having mission pressure exceeds a predetermined maximum value, usually greater than the pressure overriding the manual control at the motor.

c. An overriding device is preferably provided to regulate the pump displacement overriding the manual control setting to prevent the pump driving torque from exceeding a predetermined value.

:1. In transmissions powered by internal combustion engines, the overriding pressure limiting and torque limiting devices are preferably controllable as a function of the setting of the engine power controls, thereby providing proportional control of the motor torque at low motor speeds ,by pressure limitation, where the pump displacement is small, followed by proportional control of the pump driving torque at larger pump displacements, where engine power becomes the limitation. Also required is limitation of the highest speed ratio, by manual control of the pump and motor displacements.

e. On overrun, the functions of the pump and motor are reversed and it is necessary under these conditions to render the pressure and torque limiting devices inoperative, so that the pump and motor respond only to the setting of the manual displacement controls.

f. In some applications of hydraulic power transmissions it is necessary to override the settings of the manual displacement controls in response to some other signal, such as the temperature or speed of the power plant, or in response to the pressure drop at a flow control mechanism.

g. In high power transmissions of this type, including a boost pump, the high pressure transmission pump is liable to fail, by breakage of internal components under cavitation conditions if the boost pressure falls below a critical value due to a failure of the boost pump, and it is important to provide an overriding device to reduce the pump displacement under these conditions, so that remedial action can be taken, without damage to the expensive high pressure transmission system.

a movablepilot element to control a servo motor which is responsive to the position of the pilot element and which effects the change in displacement, and having at least one overriding control means characterized in that said overriding control means operates through another servo motor, being a primary servo motor, to vary the position of said pilot element.

By way of example, an embodiment of the above de scribed invention is described hereinafter with reference to the accompanying drawings.

FIG. 1 is a diagrammatic representation of a hydraulic transmission system of the kind to which the invention may be applied.

FIG. 2 shows one embodiment of the invention for application to the control of the system of FIG. 1.

FIG. 3 shows a second embodiment of the invention for application to the control of FIG. 1.

FIG. 4 is a view similar to FIG. 2 and illustrating the system employed in combination with a rotary-type control.

The system of FIG. 1 comprises a variable displacement pump 4, driving a variable displacement motor 5,

with a boost pump 6, boosting whichever is the low pressure duct of the transmissionthrough boost selector valves 7; a relief valve 8 discharging to reservoir 9 is employed to prevent overloading of the boost pump The displacements are varied by servo motors 10, responding respectively to the movements of a pilot control element 11, which hitherto have been manually controlled as by levers 12 to vary the displacements.

In some instances the pilot elements are in the form of rotating elements co-acting with other rotating elements, the position of which is responsive to the movements of the servo motors and hence to the displacements. Such forms of pilot control are well known and are inherently stable in operation.

Various ducts employed ,for the invention are identitied in FIG. 1 as follows:

Duct 13 is a connection from the transmission drive high pressure duct.

Duct 14 is a connection from the transmission drive low pressure duct.

Duct 15 is a duct leading to the reservoir.-

Duct 16 is a duct from the boost pump discharge.

Duct 17 is at a pressure proportional to the pump driving torque; for example, the hydro-static pressure balancing the journal loading at the pump.

For descriptive convenience it is assumed hereinafter that the elements 11 move inwards to cause an increase in the displacements and move outwards to cause a reduction in the displacements.

Referring to FIG. 2, a primary servo piston 18 slides in a cylinder 19, one end of which is fed from the boost pressure via duct 16 through a restricted orifice 20. The other end of the cylinder 19 is exhausted to the reservoir via the duct and it contains a spring 21 loading the piston 18 towards the left of the drawing. A rod 22 projecting from the piston 18 is adapted for connection to the pilot control element 11 for a pump, or to the opposite end of the lever 12 for a motor, or it may be attached to the appropriate end of a lever attached to a rotary pilot valve for the main servo system.

If there is no leakage from chamber 19A within the cylinder 19 to the left of piston 18 it will move to the right of the drawing to increase the pump displacement or to reduce the motor displacement, but it will do so only if the boost pressure is sufficient to overcome the loading of the spring 21, so that in the event of a boost failure the piston 18 will move to the left, causing the pump displacement to decrease or the motor displacement to increase, regardless of whether or not the chamber 19A is vented. This meets the requirement discussed at (g) and the spring 21 may be so rated that the maximum pump displacement is a function of the reduced boost pressure.

According to the FIG. 2 embodiment of the invention a manual control may operate to determine the maximum movement of the piston 18 to the right, as by movement of a manual control lever 23 to move a primary pilot valve 24, which is shown with grooves or flats, so that a pilot valve movement to the left vents the chamber 19A until the discharge is sealed by the resulting movements of piston 18.

Two similar overriding control valves are shown at 25 and 26. These valves are loaded by adjustable springs 25A and 26A to seal against discharge from chamber 19A and they have sealed plungers 25B and 26B subject to the pressures in ducts l3 and 17 respectively, acting to open the valves against their spring loading. Opening of the valve 25 from the drive high pressure causes the pump to stall off stroke or the motor to stall on stroke, regardless of the position of the manual control lever 23. Torque limitation is required only at the pump and is provided by the opening of valve 26 in response to the torque responsive pressure acting on its associated plunger. These simple low pressure valves meet the requirements discussed at (b) and (c); moreover the spring loading on these valves may be readily varied to suit engine control settings, so that the maximum pressure and the maximum pump torque are any desired function of the engine power. This meets the requirements discussed at (d).

Appropriate means may be provided to render the overriding control valves 25 and 26 inoperative under overrun conditions; for example, valve 27 may be provided. It is spring loaded to the open position to permit a discharge from valves 25 and 26, but which has a plunger 27B subject to the overrun high pressure from duct 14 to close the valve on overrun, thereby rendering valves 25 and 26 inoperative, so that the pump and motor displacements are then determined only by the setting of the manual control under overrun conditions. This meets the requirements discussed at (e).

The opening of any vent from the chamber 19A will cause the primary servo piston to move to override the setting of the manual control. Thus in other embodiments a duct may extend to a remote valve which may be opened by any means in response to any other overriding signal. This meets the requirements discussed at FIG. 3 shows a second embodiment of the invention, in which components similar to FIG. 2 have similar identifying numbers and in which the manual control operates through differential levers. This embodiment may be employed with the linear motion pilot element 11 of FIG. 1, but it is particularly suitable for a rotary control pilot element for the main servo motor and is described for such.

It will be assumed that rotation of the pilot element in the clockwise direction increases the pump displacement, then in the case of the pump, lever 28 is positioned by turning the rotary pilot element which controls the pump stroke and is formed on the shaft 35 to which lever 28 is affixed. Lever 29 is attached to a shaft coaxial to shaft 35, and is operated through the shaft by a manually controlled lever 30 which is externally attached to the coaxial shaft. Levers 28 and 29 are coupled to the differential lever 31, which is pivoted at the end 22 of the primary servo piston rod. Lever 28 might also operate as lever 12 when used with a control system incorporating a linear motion pilot element 11 as shown in FIG. 1. Operation of the differential levers in response to movement of motor element 22, for the same setting of lever 30, is indicated in FIG. 3.

The arrangement of the differential levers is such that, for a given position of the primary servo piston 18, movements of the manual control lever 30 produce similar movements at the lever 28 rotating the rotary pilot valve, but an outwards movement of the primary servo piston 18 changes the relationship between levers 28 and 29, sufficiently to reduce the pump displacement to zero, when the manually controlled lever is set for maximum displacement.

The primary servo piston 18 of FIG. 3 operates in the same manner as described for FIG. 2, moving to the left to reduce the pump displacement when the chamber 19 is vented, and the overriding valves 25 and 26 are similar to those described for FIG. 2.

The embodiment shown at FIG. 3 shows an alternative method for causing valves 25 and 26 to become ineffective under overrun conditions. A small plunger 32 in a cylinder is subject to the pressure in transmission duct 14. This is at boost pressure on drive, where it has no effect on the functioning of the primary servo piston 18, but duct 14 is at high pressure on overrun, so that under overrun conditions the primary servo piston 18 is held against its inward stop, regardless of whether valves 25 and 26 are open or closed and the displacement is then responsive only to the setting of the manual control. Obviously either method for causing valves 25 and 26 to become ineffective on overrun may be applied to either embodiment of the invention.

The FIG. 3 embodiment of the invention is particularly suitable for converting the function of a pump to the function of-a motor, merely by reversing the relative positions of levers 28 and 29.

rotary type, for example, of the fixed vane type, spring loaded to rotate a rotary pilot valve for the main servo motor and rotated by the primary servo pressure in the opposite direction. in this case the main control valve, forexample the manual control pilot valve, may also be a rotary valve to determine the maximum angle of rotation of the primary servo motor against the spring and overridden by overriding valves as described, to exhaust the portings to the rotary primary servo motor.

FIG. 4 shows a rotary primary servo motor 33 having a vane 34 which is a close sliding fit in the housing, forming a chamber 19 vented to the reservoir through conduit and a chamber 19a subject to the primary servo pressure, supplied through the conduit 16 and the restricted orifice 20. The primary servo motor is loaded port 37, connected throughthe drilling 38 to the low pressure chamber 19, and the end of the port opens or closes the drilling 39 to the primary servo pressure chamber 19a.

When the manually controlled. lever 36 is rotatedclockwise, the drilling 39 is closed and if there is no other vent from the chamber 19a, the primary servo motor rotates in the same direction, until the chamber is vented by the opening of the drilling39. The overriding valves 25, 26 and 27 are similar to those shownat FIG. 2 and they operate in the manner previously described, in that the opening of either valve 25 or 26 vents the chamber 190 and causes the primary servo motor to rotate clockwise, regardless of the setting of the manually controlled valve. Also the closing of the valve 27 overrides the valves 25 and 26 by causing them to become inoperative.

The invention is not limited to detail design of the primary servo motor, of the differential mechanism, or of the overriding valves. Variations in these details to achieve the same purpose would be obvious to those skilled in the art, for example, the differential levers may be replaced by differential gearing.

I claim: v

1. In a control system for variable displacement pumps, motors and the like, including a servo-motor having a pilot element operably associated therewith for control of said servo-motor in-response to positioning of said pilot element, which positioning effects changes in the displacement of the pump, motor, and the like with which it may be associated, the combination-of a main control means operative to position said pilot element, a primary servo-motor includng a cylinger having a piston mounted therein, said piston defining a chamber at one end of said cylinder, said piston being operably movable within said cylinder by pressures developed in said chambenand being operably interconnected to said pilot element whereby movement of said piston varies the position of said pilot element'in precedence to the operative effect thereon of said main control means, and vent means for reducing the pressure level withinsaid chamber, said vent m'eans including at least one vent valve having a movable valve element and a coacting valve seat, spring means resiliently urging said valve element to a closedposition against said valve seat, a variable fluid pressure to be monitored and sealed plunger means subject to said pressure to be monitored and. acting on said valve element in opposition to said spring means, whereby,

when said pressure to be monitored reaches a predetermined value, said valve element is unseated to vent said chamber.

2. The combination as specified in claim 1 further comprising overrun control means, including a nor-- mally open valve connected in series with said vent valve means and operable to close under overrun conditions to'thereby render said vent valve ineffective.

3. The combination as specified in claim 1 wherein said main control means further comprises a differential linkage connected with and operable for positioning said pilot-elemenL'the relative position of the individual links of said differential linkage being changed by movement of said primary servo-motor in overriding the setting of the pilot element.

4'. The combination as specified in claim 1 wherein said control system further comprises a boost pump, conduit means operably connecting said boost pump primary servo-motor to provide boost pump pressure in said chamber to operably move said pistons whereby failure of said boost pressures causes a variation in the position of said pilot element to reduce the displacement of the pump, motor and the like with which the same is associated.

5. The combination as specified in claim 1 wherein said control system further comprises 'a boost pump, conduit means operably connecting said boost pump to said primary servo-motor to provide boost pump pressure in said chamber, said primary servo-motor also including return loading means urging said piston in a direction toward said chamber defined, by said piston at one end of said cylinder, said boost pump pressures being sufficient to move said piston against said return loading means in a manner such that failure of said boost pressures causes avariation in the positionof said pilot element to reduce the displacement of the pump,

motor and the like with which the same isassociated.

6. The combination asspecified in claiml wherein said pressure to be monitored is the delivery pressure of the pump, motor and the like with which'the control system is associated.

7. The combination as specified in claim 6 wherein the pressure to be monitored is a pressure proportional to the driving torque of the pump, motor, and the like with whichthe control system is associated. 

1. In a control system for variable displacement pumps, motors and the like, including a servo-motor having a pilot element operably associated therewith for control of said servo-motor in response to positioning of said pilot element, which positioning effects changes in the displacement of the pump, motor, and the like with which it may be associated, the combination of a main control means operative to position said pilot element, a primary servo-motor includng a cylinger having a piston mounted therein, said piston defining a chamber at one end of said cylinder, said piston being operably movable within said cylinder by pressures developed in said chamber, and being operably interconnected to said pilot element whereby movement of said piston varies the position of said pilot element in precedence to the operative effect thereon of said main control means, and vent means for reducing the pressure level within said chamber, said vent means including at least one vent valve having a movable valve element and a coacting valve seat, spring means resiliently urging said valve element to a closed position against said valve seat, a variable fluid pressure to be monitored and sealed plunger means subject to said pressure to be monitored and acting on said valve element in opposition to said spring means, whereby, when said pressure to be monitored reaches a predetermined value, said valve element is unseated to vent said chamber.
 2. The combination as specified in claim 1 further comprising overrun control means, including a normally open valve connected in series with said vent valve means and operable to close under overrun conditions to thereby render said vent valve ineffective.
 3. The combination as specified in claim 1 wherein said main control means further comprises a differential linkage connected with and operable for positioning said pilot element, the relative position of the individual links of said differential linkage being changed by movement of said primary servo-motor in overriding the setting of the pilot element.
 4. The combination as specified in claim 1 wherein said control system further comprises a boost pump, conduit means operably connecting said boost pump primary servo-motor to provide boost pump pressure in said chamber to operably move said pistons whereby failure of said boost pressures causes a variation in the position of said pilot element to reduce the displacement of the pump, motor and the like with which the same is associated.
 5. The combination as specified in claim 1 wherein said control system further comprises a boost pump, conduit means operably connecting said boost pump to said primary servo-motor to provide boost pump pressure in said chamber, said primary servo-motor also incLuding return loading means urging said piston in a direction toward said chamber defined by said piston at one end of said cylinder, said boost pump pressures being sufficient to move said piston against said return loading means in a manner such that failure of said boost pressures causes a variation in the position of said pilot element to reduce the displacement of the pump, motor and the like with which the same is associated.
 6. The combination as specified in claim 1 wherein said pressure to be monitored is the delivery pressure of the pump, motor and the like with which the control system is associated.
 7. The combination as specified in claim 6 wherein the pressure to be monitored is a pressure proportional to the driving torque of the pump, motor, and the like with which the control system is associated. 